<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <link rel="stylesheet" href="bootstrap-3.4.1/css/bootstrap.css">
</head>
<body>

<div style="width: 400px;border: 1px solid red;">
    <div class="clearfix">
        <div class="col-xs-3">用户名</div>
        <div class="col-xs-9"><input type="text"></div>
    </div>
    <div class="clearfix">
        <div class="col-xs-3">密码</div>
        <div class="col-xs-9"><input type="text"></div>
    </div>

    <div class="clearfix">
        <div class="col-xs-offset-3 col-xs-9">
            <input type="submit" value="登录" class="btn btn-primary">
        </div>

    </div>
</div>

</body>
</html>